The present invention relates to a visual sensor system for moving objects such as vehicles and more particularly to a visual sensor system capable of extracting a characteristic feature of an object present on the path with greater ease.
In a conventional rear monitoring system for large busses, for example, a TV camera is used as a visual sensor by mounting it on the vehicle body in such a manner that its horizontal scanning line become substantially parallel to the horizontal surface of a road.
There is another conventional system in which the infrared automatic focus adjusting principle of a TV camera mounted on a vehicle (moving object) as a sensor is utilized to detect the road surface condition. This system is desired so that the sensor system mounted on the vehicle includes a light emitting device, light projecting and receiving optical systems and one-dimensional photosensor array whereby a sport light is projected toward the road surface from the light emitting device through the light projecting optical system and the scattered spot light from the road surface or an obstruction is received by the light receiving optical system, thereby determining the distance between the vehicle and the road surface or obstruction from the relation between the spot position on the one-dimensional photosensor array and the light emitting position in accordance with the principle of the triangulation. Where the inclination of the system relative to the road surface is known, the height of the light scattering point is also determined.
In this connection, as the prior art related to this type of system, the techniques disclosed in JA-A-47-44738 and JP-A48-47040 may for example be cited.
In the case of the first prior art, while an object composed of substantially vertical lines, such as, a tree, person, the vertical line elements of an automobile or the center line on the path appears in the form of a characteristic variation in the horizontal scanning line and is easily recognizable by the horizontal scanning, there is a disadvantage that any object composed of substantially horizontal lines, such as, the joint of the road pavement or the horizontal line elements of an automobile does not appear as a characteristic variation in the horizontal scanning line and is not easily recognizable by the horizontal scanning.
Where a two-dimensional planar received information is obtainable as in the case of a TV camera, while any horizontal lines can also be recognized by arranging the TV camera to scan even in the vertical direction, this gives rises to another disadvantage that to scan in both the horizontal and vertical directions requires an excessive amount of time. On the other hand, where the one-dimensional array of photosensors, e.g., one-dimensional array of charge-coupled devices (CCDs) is used in place of a TV camera employing two-dimensional array elements, depending on whether the one-dimensional array direction is selected to be the horizontal or vertical direction, it is possible to satisfactorily recognize the point of a feature of either one of an object composed of vertical lines and another composed of horizontal liens but the recognition of the point of a feature of the other is not satisfactory.
Also, int he case of the above=described second prior art or the system for detecting the surface condition of a road, there is a disadvantage that since the detection is effected by receiving the scattered light of the projected beam sport from the light emitting device, no consideration is given to such cases where the reflected light of the beam is made weak and where the disturbance light is excessively strong with the resulting deterioration of the performance. It is to be noted that the reflected light is weakened in the case of a wetted road surface on a rainy day, snowy road surface, smooth road surface or distant road surface.
Also, even in the case of this system, while it is easy to recognize an object composed of substantially vertical lines on the road, there is the disadvantage of difficulty to recognize an object composed of substantially horizontal lines on the road.